The fabrications of functional nanoarchitectures with the desired dimensional structure are of great importance because of their unique optical, electrical, magnetic and catalytic properties and have huge potential applications in electronics, sensors, optics, medicines, environments and chemical manufacturings. Current methods use traditional photolithograph, as well as more advanced soft-lithography and microfluidic techniques to shape microstructures from submicron to millimeter length scales. Except for the scanning probe microscope-based nanolithography (i.e., tip induced oxidation, dip-pen, nanografting) and biological-based assembly (i.e., molecular crossing and antibody-antigen recognition mechanisms), most of the nanometer-sized constructions were built via template-assisted and/or self-assembly procedures using molecules, clusters and particles as fundamental building blocks. The common templates used to prepare nanoscaled and nanotextured materials include patterned photoresists, polymer beads and surfactant molecules and the templates employed either top-down lithographic approach or bottom-up, self-assembly procedure.
Techniques for making nanostructured functional materials based on a polymer template have been reported in literature and patent application publications.
The most popular method for making nanostructured functional materials employs block polymer consisting of two or more different polymer chains (or blocks) that can spontaneously self-organize into nanometer-scale domains. The selective processing of one of the polymer chains or blocks using reactive ion etching has been used to produce periodic arrays at nanoscale. This method has been reported in: “Block copolymer Lighography: Periodic Arrays of ˜1011 holes in a 1 Square Centimeter” Miri Park, et. al, Science 276 (1997) pp 1401-1404; “Nanoscale patterning using self-assembled polymer for semiconductor applications”, K. W. Guarini, et. al, J. Vac. Sci. Technolo. B 19(6) (2001) pp 2784-2788; “Process integration of self-assembled polymer templates into silicon nanofabrication”, K. W. Guarini, et. al, J. Vac. Sci. Technolo. B 20(6) (2002) pp 2788-2792; “Nanostructure fabrication using block copolymer”, I W Hamley, Nanotechnology 14 (2003) pp R39-R54.
In addition, U.S. Patent Application Publication No. 2006/0134556 to Paul F. Nealey et al. describes a method for replicating substrate patterns including patterns containing irregular features. This method involves depositing block copolymer materials on a patterned substrate and ordering components in the materials to replicate the pattern. Likewise, U.S. Patent Application Publication No. 2006/0078681 to Hiroyuki Hieda et al. describes a pattern forming method using phase separation structure of self-assembling block copolymer and minimizing variations in pattern. A substrate having groove structure pre-formed thereon, is coated with a solution of the block copolymer comprising at least one block having a mesogen group. The block copolymer is caused to self-assemble in the groove to form block copolymer assemblies, which are regularly arrayed.
In an alternate approach, polymer beads are assembled to form an ordered monolayer and multi-layers on surfaces onto which a deposition can be made. Inorganic oxides with ordered nanoporous structure prepared by this method have been reported in: “A simple Method for the production of a Two-Dimensional, Ordered Arrays of Small Latex Particles”, R. Micheletto, et. al, Langmuir 11 (1995) pp 3333-3336; “Large-Scale Fabrication of Ordered Nanobowl Arrays”, Xu Dong Wang, et. al, Nano letters 4 (11) (2004) pp 2223-2226”; “Large-Size Liftable Inverted-Nanobowl Sheets as Reusable Masks for Nanolithiography”, Xu Dong Wang, et. al, Nano Letters 5 (9) (2005) pp 1784-1788”; “Direct Growth of Mono- and Multilayer Nanostructured Porous Films on Curved surfaces and Their Application as Gas Sensors”, Fengqiang, Sun, et. al, Adv. Mater. 17 (2005) pp 2872-2877”.
Besides inorganic oxides, metals, carbon nanotubes, semiconductors and other materials were also prepared. This technology has been reported in: “Nanosphere lithography: A Versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics”, Christy L., et. al, J. Phy. Chem. B 105 (2001) pp 5599-5611; “Large-scale, 2D arrays of magnetic nanopaticles”, J. Rybczynski, et. al, Colloids and Surfaces A: Physicochem. Eng. Aspects 219 (2003) pp 1-6; “Photonic Crystalls Based on Periodic Arrays of aligned Carbon Nanotubes”, K. Kempa, et. al, Nano letters 3 (1) (2003) pp 13-18; “Large-scale Hexagonal-Patterned Growth of aligned ZnO Nanorods from Nano-optoelectronics and Nanosensor Arrays”, Xu Dong Wang et. al, Nano letters 4 (3) (2004) pp 423-426.
The high cost of preparing monodispersed polymer beads, however, made this approach an expensive method. Moreover, it is difficult to obtain regular monolayer coverage for polymer beads smaller than 50 nm.
An approach to use hydrothermal treatment to nanostructured films is described in U.S. Pat. No. 6,787,198 to Shyama P. Mukherjee et al. This patent describes a method involving the hydrothermal treatment of nanostructure films to form high k PMOD™ films for use in applications that are temperature sensitive, such as applications using a polymer based substrate. The patent does not use microwave irradiation.
Although Sridhar Komarneni discloses in Current Science, Vol. 85 No. 12, December 2003, that the use of microwave field during hydrothermal and solvothermal conditions dramatically enhances their crystallization rate, oxide materials such as zirconia, titania and various spinel ferrites and metals such as Pt, Pd, Ag, Au, etc. of different sizes and shapes were crystallized using the hydrothermal, microwave-hydrothermal and microwave-solvothermal methods.
Accordingly, there has been a need to develop a cost-effective, rapid and convenient method for creating a nanotextured surface.